1. Field of the Invention
The present invention relates to a method for producing a semiconductor device which method includes growing an n-layer and a p-layer of a group III-V semiconductor on a growth substrate, bonding an electrode layer on the p-layer to a support substrate by use of solder, and removing the growth substrate through the laser lift-off process; and to a semiconductor device produced through the method. More particularly, the present invention relates to a method for producing a semiconductor device so as to prevent short circuit between side surfaces of a p-layer and an n-layer, and to protect the semiconductor device from cracking, which would otherwise occur in side surfaces of the device during the laser lift-off process; and to a semiconductor device structure produced through the method.
2. Background Art
In general, sapphire, which is chemically and thermally stable, has been employed as a substrate for the growth of a group III nitride semiconductor. However, since sapphire has no electrical conductivity, current cannot flow in a vertical direction of a semiconductor stacked structure including a sapphire substrate. Furthermore, sapphire has no clear cleavage plane, making dicing of a semiconductor structure on a sapphire substrate difficult. In addition, sapphire exhibits low thermal conductivity, and inhibits radiation of heat from a semiconductor device. In a semiconductor device including a semiconductor layer and a sapphire substrate, external quantum efficiency is low due to total reflection at the interface between the semiconductor layer and the substrate, or confinement of light in the semiconductor layer. Meanwhile, one conceivable technique for improving light extraction efficiency is forming irregularities on a light extraction surface. However, a sapphire substrate encounters difficulty in such a processing.
One technique known to solve such a problem is the laser lift-off process, which is used for separation and removal of a sapphire substrate through laser beam radiation.
Japanese Patent Application Laid-Open (kokai) No. 2005-333130 discloses a method in which a group III nitride semiconductor device is formed on a sapphire substrate; grooves are formed in the device through etching for separating the device into chips; and each group III nitride semiconductor device grown on the sapphire substrate is bonded to a support substrate, followed by the laser lift-off process. Japanese Patent Application Laid-Open (kokai) No. 2005-333130 describes that cracking in the group III nitride semiconductor device which would otherwise caused by thermal expansion of gas remaining in the grooves through laser beam radiation can be prevented by filling the grooves with a dielectric material for elimination of gas.
Japanese Kohyo Patent Publication No. 2005-522873 discloses a method in which grooves are filled with a photoresist; and, instead of bonding between a group III nitride semiconductor device and a support substrate, a metal layer is formed on the group III nitride semiconductor device, followed by the laser lift-off process. This patent document describes that grooves are filled with a photoresist for the purpose of preventing a metal from entering the grooves during formation of a layer of the metal.
Japanese Patent Application Laid-Open (kokai) No. 2006-135321 discloses a method in which a protective film of, for example, SiO2 or Al2O3, and a seed metal film are formed on inclined side surfaces of a semiconductor device; and a metal layer is formed on grooves and the semiconductor device, followed by the laser lift-off process.
During removal of a sapphire substrate through the laser lift-off process, physical impact may be applied to side surfaces of a group III nitride semiconductor device, and cracking may occur in the side surfaces. Japanese Patent Application Laid-Open (kokai) Nos. 2005-333130 and 2006-135321 and Japanese Kohyo Patent Publication No. 2005-522873 do not describe a method for preventing such physical-impact-induced cracking in side surfaces of a semiconductor device.
The method disclosed in Japanese Patent Application Laid-Open (kokai) No. 2006-135321 poses a problem in that, since a sapphire substrate (growth substrate) and a protective film are strongly bonded to each other, exfoliation occurs in the protective film during separation of the sapphire substrate, leading to cracking in a semiconductor device. This method also poses a problem in that a metal layer formed on the semiconductor device must be cut during dicing. Meanwhile, the method disclosed in Japanese Kohyo Patent Publication No. 2005-522873 or Japanese Patent Application Laid-Open (kokai) No. 2006-135321 does not employ bonding of a semiconductor device to a support substrate.
Bonding of a semiconductor device to a support substrate poses problems as described below. Formation of an n-layer on a growth substrate precedes formation of a p-layer, since the p-layer must be activated. Although the n-layer can be formed to have a large thickness, the p-layer encounters difficulty in attaining a large thickness; i.e., the p-layer has a small thickness. Thus, in a structure in which the p-layer is bonded to a support substrate by use of solder, the distance between the support substrate and the n-layer is small. Therefore, solder or metal may be deposited on side surfaces of a semiconductor device during dicing or wafer bonding, resulting in short circuit between the p-layer and the n-layer.